BIRD 60 Series Owner's manual

Brand: BIRD

Model: 60 Series

Type: Owner's manual

30303 Aurora Rd. Solon, OH 44139 Tel: 1-440-248-1200 [email protected] www.birdrf.com

Installation and Operation Manual

for the Two-Way Signal Booster System

Model Number 61-38-05

Manual No.

7-9408-2

NOTE

WARNING

Disclaimer

Product part numbering in photographs and drawings is accurate at time of printing.

Part number labels on Bird products supercede part numbers given within this manual.

Information is subject to change without notice.

Symbols

Commonly Used

CAUTION or

ATTENTION

High Voltage

Use Safety

Glasses

ESD

Electrostatic

Discharge

Hot Surface

Electrical Shock

Hazard

Important

Information

TERMS AND CONDITIONS OF SALE

Please visit

the

Bird website for complete information regarding terms

and conditions and warranty information.

http://www.birdrf.com/~/media/Bird/Files/PDF/Sales/bird-terms-and-

conditions-of-sales.ashx

First Printing: June 2005

Version Number Version Date

1 06/14/05

1.1 07/12/05

1.2 07/25/05

2 07/29/05

To satisfy FCC RF exposure requirements for transmitting

devices, a separation distance of 70 Centimeters or more

should be maintained between the UPLINK antenna of this

device and persons during device operation. To satisfy FCC

RF exposure requirements for transmitting devices, a sepa-

ration distance of 21.5 Centimeters or more should be main-

tained between the DOWNLINK antenna of this device and

persons during device operation. To ensure compliance,

operations at closer than these distances is not recom-

mended.

The antenna used for this transmitter must not be co-located

in conjunction with any other antenna or transmitter.

WARNING

For Class A Unintentional Radiators

This equipment has been tested and found to comply with the limits for a Class A digital device, pursuant to

part 15 of the FCC rules. These limits are designed to provide reasonable protection against harmful inter-

ference when the equipment is operated in a commercial environment. This equipment generates, uses,

and can radiate radio frequency energy and, if not installed and used in accordance with the instruction

manual, may cause harmful interference to radio communications. Operation of this equipment in a resi-

dential area is likely to cause harmful interference in which case the user will be required to correct the

interference at his own expense.

Changes or modifications not expressly approved by

Bird could void the user’s authority to operate the

equipment.

WARNING

This device complies with Part 15 of the FCC Rules. Operation is subject to the

following two conditions: (1) this device may not cause harmful interference and

(2) this device must accept any interference received, including interference

that may cause undesired operation.

Antenna System Installation

The antenna or signal distribution system consists of two branches. An uplink

branch typically uses an outdoor mounted, unidirectional gain antenna such

as a yagi and a downlink signal radiating system consisting of a network of

zero-gain whip antennas or lengths of radiating cable usually mounted inside

of the structure.

Even though the antenna system may not be supplied or installed by Bird

Systems. The following points need to be observed because both the safety

of the user and proper system performance depend on them.

1) Antenna system installation should only be performed by qualified techni-

cal personnel.

2) The following instructions for your safety describe antenna installation

guidelines based on FCC Maximum RF Exposure Compliance require-

ments.

3) The uplink antenna is usually mounted outside and exchanges signals

with the repeater base station or donor site. It is typically mounted perma-

nently-attached to the building wall or roof. The gain of this antenna should

NOT exceed 10 dB. Only qualified personnel should have access to the

antenna and under normal operating conditions, no one should be able to

touch or approach it within 70 Centimeters (28 inches).

4) The downlink or in-building signal distribution system is connected to the

downlink booster port using coaxial cable. The distribution system may

use radiating coaxial cable or a network 1/4 wave whip antennas whose

gain does not exceed 0 dB for any radiator. These antennas should be

installed so that the user cannot approach any closer than 21.5 Centime-

ters (9 inches) from the antenna.

Table of Contents Manual 7-9408-2 07/29/05

Table of Contents

Section 1

Introduction ......................................................................................................... 1

Note About Output Power Rating ........................................................................3

Installation............................................................................................................ 3

Cautionary Notes................................................................................................. 4

Pre-RF Connection Tests....................................................................................4

Test Equipment ...................................................................................................5

Antenna Isolation.................................................................................................5

Procedure for Measuring Antenna Isolation ........................................................ 5

Increasing Isolation..............................................................................................6

Input Signal Levels ..............................................................................................6

Procedure for Measuring Input Signal Levels......................................................6

Reduction of Incoming Signal Strength ............................................................... 8

Setting Signal Booster Gain ................................................................................8

Gain Reduction Methods ..................................................................................... 8

Bypassing Amplifier Sections ............................................................................ 9

Operation..............................................................................................................9

Signal Flow...........................................................................................................9

System Components.........................................................................................10

Passive Filtering ................................................................................................ 10

DC Regulator (3-5969) ...................................................................................... 11

OLC Assembly (3-6280)....................................................................................11

Pre-amplifier Stage (3-11423) ........................................................................... 12

Driver Amplifier Stage (3-11423) .......................................................................13

Hi Power Amplifier Assembly (3-11792)............................................................ 13

Signal Sampler (3-6999).................................................................................... 13

Signal Sampler (3-3569).................................................................................... 13

DC Junction Box (3-6254) ................................................................................. 13

Power Supply Assembly (3-15503) ...................................................................13

Performance Survey..........................................................................................14

Field Adjustments ............................................................................................. 14

Filter Tuning....................................................................................................... 15

Helical Preselectors........................................................................................... 16

Required Equipment........................................................................................16

Tuning Procedure ............................................................................................16

Bandpass Filters................................................................................................ 17

Required Equipment........................................................................................17

Tuning Procedure ............................................................................................17

Pseudo-Bandpass Filters ..................................................................................18

Required Equipment........................................................................................19

Tuning Procedure ............................................................................................19

Notch Filters ...................................................................................................... 20

Required Equipment........................................................................................20

Tuning Procedure ............................................................................................21

Single Section Amplifier Subassemblies ...........................................................22

Amplifier Tuning............................................................................................... 22

Required Equipment........................................................................................22

Adjustment Procedure .....................................................................................23

Output Level Control (OLC)...............................................................................25

Checking for Overload.....................................................................................25

Table of Contents Manual 7-9408-2 07/29/05

Maintenance and Repair ................................................................................... 26

Recommended Replacement Parts ................................................................. 26

Conversion Chart .............................................................................................. 26

Figures and Tables

Figure 1: Front view of typical 61-38-05 system ...................................................2

Figure 2: Bottom view of the cabinet enclosure....................................................3

Figure 3: Top view of the cabinet enclosure......................................................... 4

Figure 4: Measuring antenna isolation .................................................................5

Figure 5: Measuring input signal levels ................................................................7

Figure 6: Observing RF power output ..................................................................8

Figure 7: 1 stg/3 stg amplifier assembly 3-11423.................................................9

Figure 8: OLC assembly 3-6280......................................................................... 12

Figure 9: Measuring signal booster gain ............................................................ 14

Figure 10: Surveying performance ..................................................................... 15

Figure 11: Preselector tuning ............................................................................. 16

Figure 12: Observing preselector return loss .....................................................17

Figure 13: Bandpass filter tuning........................................................................18

Figure 14: The pseudo-bandpass filter............................................................... 18

Figure 15: Tuning for maximum return loss........................................................19

Figure 16: Tuning for maximun attenuation........................................................20

Figure 17: The notch filter...................................................................................20

Figure 18: Tuning for maximum return loss........................................................21

Figure 19: Tuning for maximum attenuation....................................................... 22

Figure 20: Mechanical layout of single section amplifier ....................................23

Figure 21: Measuring amplifer gain ....................................................................24

Figure 22: Meqsuring input return loss ............................................................... 24

Figure 23: Measuring output return loss............................................................. 25

Figure 24: Measuring reverse isolation ..............................................................25

Specifications ....................................................................................................27

Power Conversion Chart................................................................................... 29

Notes................................................................................................................... 32

Bird

Manual 7-9408-2 07/29/05 Page 1

INTRODUCTION

This publication, Instruction Manual 7-9408, con-

ains information to support the installation, opera-

tion, and maintenance of the model 61-38-05

signal booster system. Also included in this manual

are the procedures necessary for field adjust-

ments. It is assumed that procedures in this man-

ual will be carried out by a skilled electronics

technician who is familiar with the communications

system. This manual also gives an elementary

explanation of the operation of signal boosters and

signal distribution systems.

The 61-38-05 booster family is designed to cover

the frequency range of 138 to 174 MHz in two non

contiguous bands, One version covers 138 to 144

MHz for operation in Canada and another version

to cover 148 to 174 MHz. This version is also used

to cover U.S. land-mobile frequencies from 150.8

to 174 MHz. Units for both bands share common

active circuitry but differ in the passive filter units

that duplex the downlink and uplink branches from

a common input or to a common output. Because

signal booster systems are often times subjected

to very demanding environments with extreme con-

ditions of temperature, moisture, dirt and corro-

sives, the system is housed in a high quality

(NEMA style) enclosure. This type of housing

maintains its dimensional stability and appearance

better than other materials. Figure 1 shows a front

view of the unit with the door opened.

The system uses linear RF active amplifiers, filters,

OLC (output level control) circuitry, and DC power

sources to adequately boost the level of the RF

signals. Linear power amplifiers (Class-A) are used

in the amplifier stages of this signal booster system

in contrast to the highly efficient Class-C power

amplifiers used in the output stages of most FM

landmobile transmitters. Linear amplifiers are

biased for a relatively high continuous DC current

drain that does not change with changing RF drive

levels.

Class-A amplifiers generally have the lowest effi-

ciency of the various amplifier types, typically in the

range of 25-33%. They also draw relatively high

current levels on a continuous basis, making heat

dissipation an important factor. Their biggest

advantage is faithful reproduction of the input

waveform which results in the lowest levels of inter-

modulation distortion products (IM) of all the

classes of amplifiers. IM generation is a serious

design consideration when two or more channels

are simultaneously present in the same amplifier

stage.

Preselector filters are used in the system to provide

a number of functions including; reduction of the

level of undesired signals that may enter the sys-

tem and also help suppress any IM products that

may be inadvertently generated. They also pro-

duce a convenient impedance characteristic that

allows multiple branch paths to be tied together to

a common input/output port. This is accomplished

using critical length cables from the filter assem-

blies to a tee junction.

The output level of any signal passing through a

signal booster is determined by the input signal

level, the gain of the booster, and the maximum

output power per carrier rating of the booster. The

high power output stages used in the signal

booster may be damaged by excessive input sig-

nals. An output level control (OLC) circuit is added

to each amplifier chain to protect the amplifiers and

reduce spurious signals. The OLC circuit is

designed to maintain the maximum output level of

the booster during times of excessive input signal

levels.

OLC circuitry actuates when a predetermined max-

imum output level is reached. The output power

level in all OLC branches is sampled, and then fed

to a detector circuit which generates a DC voltage

proportional to the output power level. The DC out-

put of the detector is then applied to a control cir-

cuit which develops a voltage used to control a

variable electronic attenuator. The electronically

controlled attenuator is placed within the amplifier

signal path and reduces the incoming signal by an

amount necessary to keep the power from exceed-

ing the maximum safe level. The gain reduction

range is typically from 5 to 40 dB which is more

than adequate for most real life situations.

OLC circuitry should not be considered a panacea

for a poor system design. One undesirable affect of

OLC is that the signal level of all signals being pro-

cessed by the branch will be reduced when the cir-

cuitry is activated. This means that the

Bird

Manual 7-9408-2 07/29/05 Page 2

Figure 1: Front view of a typical model 61-38-05 signal booster system.

Backup Battery

connects here

Filtering

Signal

Sampler

3-3569

Signal

Sampler

3-3569

Signal

Sampler

3-6999

Signal

Sampler

3-6999

OLC

Assembly

3-6280

OLC

Assembly

3-6280

1 stg/3 stg

Amplifier

Assembly

3-11423

1 stg/3 stg

Amplifier

Assembly

3-11423

High Power

Amplifier

Assembly

3-11792

High Power

Amplifier

Assembly

3-11792

Regulator

3-5969

Regulator

3-5969

Power Supply

Assembly 3-11503

RF In/Output

Connector

RF In/Output

Connector

Bird

Manual 7-9408-2 07/29/05 Page 3

performance of the system is actually decreased

on all other channels within the branch as long as

gain reduction is taking place. This implies that

OLC has been designed to handle short term or

transient overdrive episodes only.

Note About Output Power Rating

A single maximum output power rating does not

apply to broadband signal boosters because the

linear amplifiers (Class A) used in them may have

to process multiple simultaneous signals. Under

these conditions, the questions of power rating

becomes more complex.

When more than one signal is amplified, a number

of spurious signals will also appear in the amplified

output. They are referred to as intermodulation dis-

tortion products, more commonly called I.M. These

spurious products would not be present in a per-

fectly linear amplifier but as in all things, something

short of perfection is realized. The net result is that

the total power out in each signal will be somewhat

less than the single carrier rating in order to main-

tain adequate I.M. performance.

INSTALLATION

The layout of the signal distribution system will be

the prime factor in determining the mounting loca-

tion of the signal booster enclosure. However,

safety and serviceability are also key consider-

ations. The unit should be located where it cannot

be tampered with by unauthorized personnel yet is

easily accessible to service personnel using trou-

ble shooting test equipment such as digital multim-

eters and spectrum analyzers. Also consider the

weight and size of the unit should it become

detached from its mounting surfaces for any rea-

son.

Very little is required to install this signal booster.

The unit should be bolted in its permanent position

using lag bolts or other suitable fasteners. Make

sure there is an unobstructed airflow over the

external heatsinks. Safety and serviceability are

key considerations. The signal booster cabinet will

stay warm during normal operation so in the inter-

est of equipment longevity, avoid locations that will

expose the cabinet to direct sun or areas where the

temperature is continually elevated.

The signal booster is designed to be powered from

120 VAC and a conduit entry box is provided at the

bottom of the enclosure for bringing the AC line

into the cabinet. AC line connections should be

made in accordance with local electrical and build-

ing codes. The battery backup system should also

Figure 2: Bottom view of cabinet enclosure.

Bird

Manual 7-9408-2 07/29/05 Page 4

be connected at this time. The 3-pin MS style con-

nector for the backup power system is labeled and

is located on the bottom of the enclosure. A photo-

graph of the bottom of the cabinet is shown in Fig-

ure 2.

Connection of RF to the unit is made via “N” female

connectors located on top of the cabinet. These

connectors are individually labeled “High Frequen-

cies IN Low frequencies OUT” and “Low Frequen-

cies IN High Frequencies OUT”. Care should be

used when making connections to these ports to

insure the correct antenna cable is connected to its

corresponding input / output port or the system will

not work. The use of high quality connectors with

gold center pins is advised. Flexible jumper cables

made of high quality coax are also acceptable for

connecting to rigid cable sections. A photograph of

the top of the cabinet is shown in Figure 3.

CAUTIONARY NOTES

The following cautions are not intended to frighten

the user but have been added to make you aware

of and help you avoid the areas where experience

has shown us that trouble can occur.

Just like the feedback squeal that can occur

when the microphone and speaker get too close to

each other in a public address system, a signal

booster can start to self oscillate.

This will occur

when the isolation between the input antenna or

signal source and the output antenna or signal dis-

tribution system does not exceed the signal

booster gain by at least 10 dB. This condition will

reduce the effectiveness of the signal booster and

possibly damage the power amplifier stages.

The major cause of damage to signal boosters is

the application of input RF power levels in excess

of the maximum safe input.

This can happen inad-

vertently when connecting a signal generator with

full power out to one of the inputs or by a very

strong signal that is far stronger than expected.

The Maximum Safe Power input level for your unit

can be found on the laminated tag affixed to the

top of the cabinet near the RF input/outputs. Fol-

lowing the pre-installation checks listed below will

help to avoid these two problems.

PRE-RF CONNECTION TESTS

Certain characteristics of the signal distribution

system should be measured before connecting it to

the signal booster. This step is necessary to insure

that no conditions exist that could possibly damage

the signal booster and should not be skipped for

even the most thoroughly designed system. Two

characteristics need to be measured; antenna iso-

lation and input signal levels.

Figure 3: Top view of cabinet enclosure.

Bird

Manual 7-9408-2 07/29/05 Page 5

Test Equipment

The following equipment is required in order to per-

form the pre-installation measurements.

1) Signal generator for the frequencies of interest

capable of a 0 dBm output level. Modulation is

not necessary.

2) Spectrum analyzer that covers the frequencies

of interest and is capable of observing signal

levels down to -100 dBm.

3) Double shielded coaxial test cables made from

RG142 or RG55 coaxial cable.

Antenna Isolation

Antenna isolation is the signal path isolation

between the two sections of the signal distribution

system that are to be connected to the signal

boosters antenna ports. Lack of sufficient isolation

between the input and output antennas can cause

the amplifiers in the system to oscillate. This can

happen at a high enough level to damage the

power amplifier stages. In general, if one or both

antenna ports are connected to sections of radiat-

ing coaxial cable (lossy cable) via short jumpers of

non-radiating cable the isolation will be more than

adequate because of the high coupling loss values

that are encountered with this type of cable. When

a network of antennas are used for the input and

output, this problem is much more likely. Isolation

values are relatively easy to measure with a spec-

trum analyzer and signal generator.

Procedure for Measuring Antenna Isolation

1) Set the signal generator for a 0 dBm output

level at the center frequency of one of the signal

boosters passbands.

2) Set the spectrum analyzer for the same center

frequency and a sweep width equal to or just

slightly greater than the passband chosen in

step one.

3) Connect the test leads of the signal generator

and the spectrum analyzer together using a

female barrel connector, see Figure 4. Observe

the signal on the analyzer and adjust the input

attenuator of the analyzer for a signal level that

just reaches the 0 dBm level at the top of the

graticule.

INTERNAL

SIGNAL DISTRIBUTION

SYSTEM

SPECTRUM

ANALYZER

EXTERNAL

ANTENNA

SIGNAL

GENERATOR

ZERO LOSS

REFERENCE

ISOLATION (dB)

Figure 4: Typical test equipment setup for measuring antenna isolation.

Bird

Manual 7-9408-2 07/29/05 Page 6

4) Referring to figure 4, connect the generator test

lead to one side of the signal distribution system

(external antenna) and the spectrum analyzer

lead to the other (internal distribution system)

and observe the signal level. The difference

between this observed level and 0 dBm is the

isolation between the sections. If the signal is

too weak to observe, the spectrum analyzer's

bandwidth may have to be narrowed and its

input attenuation reduced. Record the isolation

value. The isolation value measured should

exceed the amplifier gain figure by at least

15 dB.

It is wise to repeat the procedure listed above for

measuring antenna isolation, with the signal gener-

ator set to frequencies at the passbands edges in

order to see if the isolation is remaining relatively

constant over the complete width of the passband.

Also, the procedure should be repeated for each of

the remaining channels in the system.

Increasing Isolation

If the measured isolation does not exceed the

amplifier gain figure by at least 15 dB then modifi-

cation of the signal distribution system is required.

Alternately, the gain of the signal booster can also

be reduced to insure the 15 dB specification is met.

If the isolation cannot be increased then the

amount of gain reduction required is determined as

shown in the following example.

Input Signal Levels

Excessive input signal levels can damage the sig-

nal booster. Although this problem is less severe in

OLC protected branches, strong signals may

cause sudden reductions in gain and an associ-

ated decrease in the desired output signal

strength. Even in the most carefully designed sig-

nal distribution systems, unpredictable situations

can arise that can cause this trouble. A few of the

more common causes are:

a) Unintended signals entering the system. Prima-

rily caused by radios operating on channels that

are within the operational bandwidth of the sig-

nal booster. Sometimes this will be a transient

problem caused by mobile units when they

transmit while in close proximity to your system.

b) Hand-held and mobile units that approach

much closer than expected to one of the anten-

nas in the signal distribution system.

c) Unexpected signal propagation anomalies.

Building geometry can cause signal ducting and

other phenomena that cause signal levels that

are much stronger (or lower) than expected.

d) Lower than estimated signal attenuation causes

signals to be unusually strong. Higher losses

can also occur giving weaker signals than

desired.

e) Signal booster model with excessive gain. In

systems that have an existing signal booster, it

is sometimes assumed that an identical unit

should be installed when expanding the system

to provide extended coverage. In most cases, a

signal booster with far less gain than the first is

required.

f) Improper installation or application of signal

splitters or directional couplers in the signal dis-

tribution system. This is usually the cause of too

low a signal level but deserves mentioning

here. Signal splitting needs to be done with con-

stant impedance signal splitters so that the

proper power splitting ratios and VSWR are

maintained. Using tee connectors by them-

selves is inviting trouble. Directional couplers

must be connected with regard to their direc-

tionality and coupling levels or improper system

signal levels may result.

Procedure for Measuring Input Signal Levels

1) Set a spectrum analyzer for the center fre-

quency of one of the branches (look at the

specification drawing for this information).

2) Set the analyzer sweep width so that the entire

passband frequency range can be observed.

EXAMPLE

Gain Reduction (dB) = Minimum Isolation (dB) -

Measured Isolation (dB)

If the measured isolation is -75dB and the mini-

mum isolation is -80dB then the amount of gain

reduction required is: -80dB - (-75) = -5 dB

Bird

Manual 7-9408-2 07/29/05 Page 7

3) The analyzer input attenuator should be set to

observe input signal levels from approximately -

80 dBm to 0 dBm.

4) Connect the analyzer to the section of the sig-

nal distribution system that is going to serve as

the input for the branch you want to observe

(see Figure 5).

5) Record the power level (in dBm) of all carriers

in the passband frequency range that are signif-

icantly greater than the noise floor displayed on

the analyzer.

6) Repeat steps 1 through 5 for the remaining sig-

nal booster channels.

7) To find the total power being applied to the

channel, the calculations listed below must be

performed. The conversion chart at the rear of

the manual can be used. Here are the steps:

a) Convert all values in dBm to Watts

b) Total the power for all carriers in Watts

c) Convert the total power in Watts to dBm

Repeat the calculation for all of the branches in the

system. For example: suppose we have a signal

booster with a maximum gain of 70 dB. After

checking the input signal levels, it was determined

that there are three signals that are significantly

greater than the noise floor displayed on the ana-

lyzer. These signals have strengths of -45 dBm, -

43 dBm and -41 dBm.

First we use the conversion chart at the end of this

manual to convert the power levels in dBm to watts

so that we can add them together. The power in

watts is written in scientific notation but the chart

uses computer notation. For example, in the chart,

an exponent may be written as E-08. In conven-

tional mathematical notation E-08 is written 10

-8

The total power must be written as a number

between 0 and 10 to use the chart. Look up

1.611E-7 in the Watts column. This number falls

between -38 and -37 dBm so we chose -37

because it is the next higher value.

Power (dBm) Power (watts)

-45 dBm

3.16 x 10

-8

-43 dBm

5.01 x 10

-8

-41 dBm

7.94 x 10

-8

TOTAL

16.11 x 10

-8

S p e c t r u n y z e r

R d i o 1

R d i o 2

S I G ˘ ˇ ˆ I S ˙ R I ˝ ˛ ˙ I ° ˘ S ˜ S ˙ !

Figure 5: Typical test equipment setup for measuring input signal levels.

Bird

Manual 7-9408-2 07/29/05 Page 8

Reduction of Incoming Signal Strength

Reducing the strength of offending signals may

require some or all of the following steps:

The addition of extra filtering. Consult Bird

ales engineers for help in this respect.

b) Modification of the signal distribution layout by

changing the type or location of pickup anten-

nas. This has to be approached in an empirical

way, that is, change-and-try until you get the

desired results. Sometimes changing from omni

to directional antennas will correct the problem.

Setting Signal Booster Gain

The Pre-Installation checks as outlined earlier

should have been performed to determine if gain

reduction will be necessary for your installation.

This can be due to low antenna isolation or exces-

sive input signal levels, or both. The actual amount

of gain reduction is determined by the largest num-

ber required because of either low isolation or

excessive signal levels.

For example, if the results of the isolation measure-

ment indicated the need for a gain reduction of -10

dB but signal level measurements indicate a need

for only a -5 dB gain reduction; then 10 dB is the

number required since both conditions are satis-

fied.

Gain Reduction Methods

As shipped from the factory, the system was setup

for maximum gain. Gain reduction is accomplished

by adding fixed attenuator pads or where even

greater reductions are required by bypassing one

section in a multi-section amplifier stage. Bypass-

ing of amplifier sections is preferred for large gain

reductions so that excessive noise levels are not

produced. Use of attenuator pads alone will reduce

gain but the signal booster will also amplify the

noise generated in the lower level sections.

The addition of attenuator pads may be necessary

in order to achieve the proper signal levels in the

overall communications system. This is quite com-

mon as actual signal losses in a radiating cable

system can vary somewhat from predicted theoret-

ical values. Fine adjustment of gain in communica-

tions systems with cascaded signal boosters can

be very important to keep performance uniform

over the entire length of the system.

Figure 6 shows the use of a spectrum analyzer to

monitor signal levels in a signal booster. The ana-

lyzer connects to the signal sampler on the output

end of the branch to be tested. Attenuation is then

adjusted for the proper signal levels factoring in the

RF from Antenna or

Previous Repeater Amplifier

Signal Distribution System

FilterFilter

Sampler

Variable

Attenuator

Spectrum

Analyzer

10 dB Pad

Amp

Figure 6: Observing RF power output of a signal booster using a spectrum analyzer.

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Manual 7-9408-2 07/29/05 Page 9

-50 dB coupling loss of the signal sampler and any

additional loss produced by attenuator pads on the

analyzer input. A pad on the analyzer input can

help to minimize measurement errors due to

VSWR mismatch that occurs with some analyzers.

A pair of fixed attenuator pads (3 and 6 dB) are

supplied for the purpose of gain reduction. They

are mounted in clips to the top of the filter assem-

blies in the center of the unit. The pads’ attenuation

values are clearly labeled on the body of the atten-

uator. The correct position for adding fixed pads to

the system is at the input or output of the electronic

attenuator ports on the OLC assembly (shown as

the dotted outline symbols on the specification

drawing).

CAUTION: Any fixed attenuator

pads that are already connected into

the booster circuitry have been

installed at the factory and should

not be removed for any reason. Their

function may be other than gain

reduction.

BYPASSING AMPLIFIER SECTIONS

Sometimes the amount of gain reduction needed is

greater than the amount available with the fixed

attenuator pads alone. In this case, the first stage

of the three stage portion of amplifier assembly (3-

11423) in the uplink or downlink branch may be

bypassed. The individual stages of these multi-

stage amplifiers are connected together with short

lengths of coaxial cable. To bypass the first stage

of the driver amp remove the coax cable that inter-

connects the first and second stages of the driver

amplifier (see Figure 7). Move the input cable from

the input connector on the first stage to the corre-

sponding connector on the second stage of the

driver amp. The BNC RF input connector for each

amplifier stage is located furthest from the DC input

TNC connector. Keep in mind that the total gain

reduction is the sum of the added padding plus the

loss of gain for the bypassed amplifier section.

Quality 50 ohm terminations should be installed on

the open terminals of any bypassed stage.

OPERATION

It is imperative that the pre-installation checks be

performed as outlined earlier. Failure to do so may

lead to unsatisfactory operation or damage to the

signal booster. All that is required in order to put

the system into operation after the installation is to

turn on the power supply assembly. The green

LED on the power supply will illuminate indicating

normal operation. If the red LED on the power sup-

ply assembly illuminates it indicates operation from

the backup power source.

SIGNAL FLOW

Signal flow through the system is illustrated using

the system block diagram that is shown in specifi-

cations drawing shipped with your system. The 61-

38-05 model signal boosters are composed of 2

branches, uplink and downlink. Because the uplink

and downlink branches are physically identical,

Pre-Amp

(Single Stage)

Driver Amp

(3 Cascaded Stages)

Output

Input

Output

Input

Figure 7: 1stg/3stg amplifier assembly 3-11423.

Bird

Manual 7-9408-2 07/29/05 Page 10

both being constructed from the same set of sub-

assemblies, the signal flow discussion that follows

is applicable equally well to both branches. The

only difference between the two branches is the

tuning of their passbands.

Signals enter the system through the RF connec-

tors at the top of the cabinet. This is where the cus-

tomers antenna system is interfaced to the

booster. Input signals are immediately passed

through passive filtering. The filter configurations

can vary slightly depending on the exact model of

booster. The filters provide the necessary isolation

to allow a pair of amplifier chains to be tied

together providing bi-directional amplification with

a single common input and common output con-

nection. A secondary but very beneficial effect of

filtering is instantaneous input and output fre-

quency spectrum limiting which helps to prevent

amplification of unwanted channels. After filtering

signals are then applied to a preamplifier stage (the

first section of the multi-stage amplifier assembly

3-11423).

Following the preamplifier signals are applied to

the input of OLC (output level control) assembly 3-

6280. This assembly will attenuate the incoming

signals if necessary, to protect the final amplifier

from being overdriven by stronger than usual input

signals. The amount of attenuation is determined

by a reference voltage produced by a detector cir-

cuit built into the OLC assembly, which continu-

ously samples the output level of the final amplifier.

Once past the OLC assembly the signals are

applied to a driver amplifier composed of the final

three sections of the multi-stage amplifier assem-

bly 3-11423. The driver amplifier ensures that sig-

nals applied to the next stage, the final amplifier,

are at their optimum level and as free of any inter-

modulation distortions as possible. The high power

amplifier 3-11792 is a linear amp operated at con-

siderably less than it’s maximum output power to

insure maximum linearity.

Signals output from the high power amplifier stage

are routed to the detector input of the OLC assem-

bly by the first signal sampler 3-6999. The purpose

of the detected signal is to adjust the amount of

attenuation provided by the OLC assembly to the

incoming signal after the preamplifier stage. The

output of the high power amplifier is passed

through a second signal sampler 3-5969 that pro-

vides a -50 dB sampled signal as a convenience

for service technicians. The signals then pass

through passive filtering before leaving the signal

booster at the output connector located on the top

of the cabinet. This is where the customers

antenna system is interfaced to the booster.

SYSTEM COMPONENTS

Each of the major system components used in the

model 61-38-05 family of signal boosters are briefly

discussed in the following text. Refer to the system

specification drawing that shipped with your sys-

tem during this discussion. The specification draw-

ing will include complete electrical and mechanical

specifications for your model. These include fre-

quency band, bandwidth, power gain and maxi-

mum power ratings. Recommended maximum

power ratings are shown for single signal and mul-

tiple signal applications.

The functional block diagram included on the spec-

ification drawing shows all of the major subassem-

blies and their interconnections. Part numbers for

the major assemblies are also shown. We suggest

you look this drawing over carefully to fully familiar-

ize yourself with the unit.

Passive Filtering

The passive filters on the input and output ends of

each active section have one major purpose: they

provide the necessary isolation to allow a pair of

amplifier chains to be tied together providing bi-

directional amplification with a single common

input and common output connection. The filters

provide duplex operation and each one is tuned to

pass either the downlink or uplink frequency band.

They must provide a minimum isolation factor that

exceeds the amplifier gain by 15 dB in order to pre-

vent regenerative feedback and maintain spurious-

free operation. In the VHF spectrum, these filters

are usually constructed from cascaded coaxial

bandpass cavities or multistage helical bandpass

filters. Bandpass filters may be augmented by

notch filters using the same basic resonator style

(coaxial or helical). Notching filters allow the filter

response to be closely tailored to the specific isola-

tion requirements for the specific uplink and down-

link frequency band separation. Typical VHF

frequency pairs (repeater input/output frequencies

= Down/uplink frequencies) vary considerably in

frequency separation making flexibility in tailoring

the filter response a necessity for proper operation.

When necessary, single channel bandpass filters

may also be used as an augment to facilitate close-

spaced frequency operation without interference.

Bird

Manual 7-9408-2 07/29/05 Page 11

Single channel bandpass filters are generally 4-

pole crystal filters using piezo-electric resonators.

A secondary but very beneficial effect of filtering is

instantaneous input and output frequency spec-

trum limiting which helps to prevent amplification of

unwanted channels.

While filtering can reduce or eliminate spurious

output signal, this is a tertiary function in the VHF

signal booster because this booster family uses

Class-A linear amplifiers that generate much lower

harmonic content than the typical Class C or D

amplifier used in typical landmobile transmitters.

The input and output filter assemblies used in the

model 61-38-05 signal booster systems are com-

posed of helical preselectors, 2” square bandpass

cavities, and 2” square notch cavities. These filters

all have a carefully shaped response curves that

define the pass windows for the booster.

The helical preselectors are composed of four cas-

caded helical cavities. The cavities are intercon-

nected with critical length cables to synthesize a

shaped response. The bandpass filters pass one

narrow band of frequencies (the passband) and

attenuate all others with increasing attenuation

above and below the pass frequencies. The inser-

tion loss setting determines the filters selectivity

and maximum power handling capability. Insertion

loss is set at the factory. The notch filters are used

to notch out a very narrow range of frequencies

and improve the skirt selectivity of associated

bandpass filters.

The filters used in the booster are factory pretuned

and do not require any adjustment. The filters are

easy to misalign. Being passive devices using sil-

ver plated contacts means they requires no main-

tenance and will stay tuned indefinitely unless they

are physically damaged or tampered with. If it is

suspected that a filter is out of alignment, we sug-

gest returning it to the factory for re-alignment.

However, if the necessary test equipment is avail-

able then the tuning procedure outlined later in this

manual may be used to put it back on frequency.

DC Regulator (3-5969)

The DC regulator receives 24.7 VDC from the

power supply assembly through it's input 'TNC'

connector. Two regulator assemblies are used,

one for each signal branch in the bi-directional sys-

tem. each of the regulators provides two different

output voltages, +15 VDC and +21.7 VDC. A mini-

mal voltage differential of 3 volts is required

between the input and the output of the 3-5969

regulator in order to maintain proper operation. The

regulator assembly can provide up to 5 amps of

total current.

The regulator circuit uses two conventional IC reg-

ulator chips. An LM338K is used to produce the

fixed 15 VDC, and an LM340K is used for the vari-

able output which is factory adjusted to +21.7 VDC.

Test jacks (red & black) are available on the regu-

lator chassis for measuring the input, fixed-output,

and the variable-output voltages. The regulator has

an access hole on the side of it's case for adjusting

the variable-output voltage. A thin blade screw-

driver is used to engage a trim-pot type variable

resistor R2 which is then rotated until the desired

output voltage is obtained. Adjustment of the regu-

lator is only required after making repairs to the

regulator circuitry.

OLC Assembly (3-6280)

The OLC assembly 3-6280 is used in both

branches of the system is divided into three

shielded compartments; one housing the RF to DC

converter, the second a DC control circuit, and the

third containing the PIN diode attenuator circuit. A

test point is provided for measuring the voltage that

is applied to the PIN diode attenuator. A second

test point allows measurement of the voltage sup-

plied by the converter to the DC control circuit (see

Figure 8). Regulated 21.7 VDC is supplied to the

"TNC" female connector to power the assembly.

The RF to DC converter receives RF from the sig-

nal sampler and produces a negative polarity DC

output voltage that is proportional to the RF signal.

A Schottky Barrier diode is used as the detector.

Because this detector circuit has a very high input

impedance, the magnitude of the voltage that it

produces will vary if the length of the coaxial cable

which connects it to the signal sampler changes.

Therefore, it is important not

to change this length.

The voltage produced by the RF to DC converter is

directly proportional to the output signal strength of

the final amplifier. The voltage is supplied to the

DC control circuit at the non-inverting terminal of

op-amp IC2. A variable reference voltage is

applied to the inverting terminal of the same op-

amp. Variable resistor VR2 is used to set the mag-

nitude of this reference voltage and controls the

level at which gain reduction will start to occur. As

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BIRD 60 Series Owner's manual

BIRD 60 Series Owner's manual

BIRD 60 Series Owner's manual

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